Usually, these embedded appliances are composed of a sealed outer body, closed by a transparent element, for example in glass, crossed by the beam of light of the internal optical system. The appliance is normally equipped with an embedding well that is cemented into the ground to form the compartment in which the appliance is embedded.
The body/well system must meet various requirements, such as a high degree of IP protection, the ability to be walked on/driven over, embedding depth and diameter, IK protection (against shock or acts of vandalism) and theft, maximum temperature of the parts that can be touched, flush or protruding finishing rings, orientability of the beam.
Since the “inground” embedded appliance is designed for installation in an exact point on the ground and/or at a certain distance from the object to be illuminated (wall, tree, etc.), except when the light is widely diffused, the beam of light must be orientable both on the horizontal plane and with respect to a vertical axis. This orientability of the beam of light is also known as pointing.
The ranges of angles covered are normally from −90° to +90° in the horizontal plane and from 0° to 30° with respect to the vertical axis.
As to the first adjustment, achieving horizontal pointing by rotating the outer body in the well is to be avoided since the two elements have a fixed locking system, and to avoid the aesthetic elements of the body or of the outer ring of several appliances in a row from be oriented randomly and/or otherwise.
It is therefore preferable for the internal optical system to be orientable in the two directions.
With traditional sources (discharge lamps, halogen) the orientation of the optical unit is obtained simply by means of “gimbal” systems in various different shapes, but traceable to a rotating interface which houses an oscillating optical body.
As known, with LED light sources the thermal dissipation of the absorbed power not converted into light is crucial. The heat transfer is concentrated at the base of the LED and must be guaranteed to maximise the light output, the efficiency and durability over time of the device and of its performance.
In an inground light, closed by a poorly conductive element (glass and relative attachment ring), the most efficient way to dissipate the heat produced by the source is to transmit it to the surrounding ground through the metal body, the minimum air interspace between the body and the well, and lastly the well itself.
The difficulty is thus to transmit the heat from the LED to the metal body (in general to the external parts) when the LED is mounted on a rotating/oscillating gimbal structure.
Some solutions to this problem have been proposed.
One solution is to limit the ratio between the power of the LEDs and the size of the necessary body (i.e. using low power or enlarging the body); this makes it possible to keep said body and thus the air inside it “colder”. This choice, however, is contrary to the small recess size requested in installations and to the production costs.
A second solution is to create large contact sections between the rotating elements and the body. This solution has the disadvantage of requiring heavy and expensive elements and expensive machining (milling, boring) of the contact surfaces to be made.
In a third solution a local, mobile heatsink is used for the LED and the heat exchange with the fixed body is increased via an internal air stirrer, such as a fan. Disadvantages of this solution are the additional costs, possible fan noise, increased exposure to failures, and market distrust of active dissipation.
It is evident therefore that the solutions proposed to date do not definitively solve the problem of heat dissipation of an “inground” lighting device with orientable lighting beam and in particular with an LED lighting source.